1. Technical Field
The present invention relates to electro-optical devices, such as liquid crystal display devices, and electronic apparatuses.
2. Related Art
In general, an active matrix liquid crystal display device is well known as an example of an electro-optical device. The active matrix liquid crystal display device includes a plurality of scanning lines and common lines, a plurality of data lines which perpendicularly intersect the plurality of scanning lines and common lines, a first substrate having a plurality of pixel circuits arranged thereon so as to correspond to intersections of the scanning lines and the data lines, a second substrate arranged so as to face the first substrate, and a layer of liquid crystal which is an electro-optical material arranged between the first substrate and the second substrate.
The liquid crystal display device further includes a scanning line driving circuit which drives the scanning lines and a data line driving circuit which drives the data lines.
Examples of methods of driving liquid crystal include a TN (twisted nematic) method, a VA (vertical alignment) method, and an IPS (in-place-switching) method.
Here, the VA method will be described with reference to FIGS. 8A to 8C. In the VA method, when a voltage is not applied, liquid crystal molecules are aligned substantially upright with respect to the horizontal direction whereby light emitted from a backlight arranged on a back side is blocked and black display is attained (FIG. 8C). When a voltage having a predetermined value (an intermediate value) is applied, the liquid crystal molecules are aligned so as to be at a predetermined angle with respect to the horizontal direction whereby part of the light emitted from the backlight arranged on the back side is transmitted (FIG. 8B). When a maximum voltage is applied, the liquid crystal molecules are flatly aligned with respect to the horizontal direction whereby the light emitted from the backlight arranged on the back side is entirely transmitted and white display is attained (FIG. 8A).
Furthermore, in the VA method, when a voltage is not applied, since the light emitted from the backlight is not influenced from the liquid crystal molecules and is substantially blocked by a polarizing plate, pure black display is attained when compared with the TN method, and furthermore, a high contrast ratio is attained.
Furthermore, in the VA method, when compared with a response speed in a rise time (a change from black display to white display) and a response speed in a fall time (a change from white display to black display), a response speed when a halftone is displayed is intend to be low. To improve the response speed when a halftone is displayed, in general, overdrive processing is performed (for example, refer to JP-A-2003-143556).
Here, the overdrive processing will be described. The liquid crystal display device detects gray-scale data from an input image signal and supplies the detected gray-scale data to a correction circuit and a memory. The memory stores the gray-scale data for a period of one frame and outputs the gray-scale data to the correction circuit.
The correction circuit compares gray-scale data in a preceding frame with gray-scale data in a succeeding frame, corrects the gray-scale data in the succeeding frame in accordance with a result of the comparison, and applies a voltage to a liquid crystal panel in accordance with the correction. Accordingly, the response speed when halftone is displayed is improved by applying a large voltage to the liquid crystal panel.
However, for such overdrive processing, a memory is required for temporarily storing the gray-scale data in the preceding frame. Therefore, when a liquid crystal display device including a driving processing unit which is not provided with a memory such as a RAM (random access memory) is used, a memory dedicated to the overdrive processing is required to be provided. Accordingly, an area of a substrate for implementing the memory becomes large resulting in increased cost.
Furthermore, in the overdrive processing, an electric power is required for comparison and calculation of the gray-scale data in the preceding frame and the gray-scale data in the succeeding frame.